This invention relates to an elastic electroconductive product, more particularly to an elastic product which has been rendered electroconductive for use as electrical materials and as rollers for transferring electrostatic latent images in electrophotographic copiers, the elastic electroconductive product comprising a soft elastic material such as rubber, synthetic resin or the like and an electroconductive film formed thereon and having a desired electric resistivity for example in the range of 10.sup.12 to 10.sup.2 ohms.
Conventionally known are elastic products which have been rendered electroconductive for use as electroconductive rollers and belts in electrophotographic copiers, printing presses, spinning machines, etc. for antistatic purposes or for injection of electric charges. Such electroconductive products are prepared by mixing or kneading an antistatic agent predominantly comprising an anionic, cationic, nonionic or ampholytic surfactant with a soft elastic material such as natural rubber, synthetic rubber or synthetic resin and shaping the mixture. With these products, the hygroscopic or electroconductive properties of the surfactant are utilized.
Electroconductive products of another type are also known which are prepared by shaping an elastic material such as described above and incorporating therein a fine powder of carbon black or metal such as aluminum, silver, nickel, copper or the like for antistatic purposes. These electroconductive products therefore utilize electroconductive properties of carbon black, metal or the like.
However, the elastic products thus rendered electroconductive generally have a relatively high electric resistivity of 10.sup.12 to 10.sup.9 ohms and are not fully effective in antistatic or charge injecting action for example as an electrostatic latent image transfer roller referred to above which must have a sufficiently low resistivity.
Since it is impossible to lower the electric resistivity of the electroconductive elastic product to the desired value only by mixing or kneading an antistatic agent such as surfactant with the elastic base material, there is a need to incorporate a large amount of finely divided electroconductive material. The electric resistivity will then be reduced, but the addition of the fine powder impairs the softness of the elastic electroconductive product obtained, rendering the elastic product harder and brittle to reduce its elasticity a great deal. Consequently, when used for example as the transfer roller, the product fails to assure an elastic, uniform contact pressure over a long period of time against copy paper or like opposing member with which it comes into contact.
In other words, there has been a limitation on the amount of the antistatic agent or electroconductive material to be added to rubber or like soft elastic material for the improvement of the electroconductivity thereof.
To assure an especially elastic, uniform contact pressure, a spongy elastic product having a low electric resistivity may be made by adding great amounts of a highly electroconductive material such as metal powder and a foaming agent such as ammonium carbonate, diazoaminobenzene, hydrazide benzensulfonate or the like to a synthetic rubber or like elastic material and foaming the resulting mixture, but the fine metal powder markedly reduces the elasticity of the resulting spongy product and its ability to contact intimately. Thus it is impossible to obtain a sponge-like elastic product having numerous uniform pores therein.
It is also known to form an electroconductive film by applying to a base material an electroconductive coating composition comprising epoxy resin and silver or the like dispersed therein with an organic solvent. However, this method is expensive and has the drawback that the organic solvent is inflammable and harmful to the human body because of its toxicity and attacts rubber or like base material.
The electroconductive member such as a roller for transferring electrostatic latent image in an electrophotographic copier is intentionally biased to inject an electric charge from the ground into charged copy paper or like opposing member. It is therefore desired that electrically the conductive member have a relatively low resistivity, for instance, of 10.sup.8 ohms, preferably 10.sup.5 ohms, while mechanically it must be adapted for contact with the opposing member under uniform pressure to bias the same by injection of an electric charge without permitting uneven injection of charge due to the frictional resistance of an irregular surface. Moreover, it must have soft and elastic properties equivalent to or exceeding those of usual rubber (up to about 50.degree. SR) so as not to damage the opposing members (copy paper and pinch roller) when brought into contact therewith.